The invention relates generally to integrated circuit fabrication and semiconductor devices and, in particular, to methods for designing and fabricating a bipolar junction transistor.
Bipolar junction transistors are found, among other end uses, in high-frequency and high-power end use applications. In particular, bipolar junction transistors may be used in microwave power amplifiers found in wireless communications systems and in power amplifiers found in mobile devices, as well as high-speed logic circuits. Bipolar junction transistors are three-terminal electronic devices that include semiconductor regions defining an emitter, a base, and a collector. An NPN bipolar junction transistor includes regions of n-type semiconductor material constituting the emitter and collector, and a region of p-type semiconductor material constituting the base situated between the regions of n-type semiconductor material. Similarly, a PNP bipolar junction transistor includes regions of p-type semiconductor material constituting the emitter and collector, and a region of n-type semiconductor material constituting the base situated between the regions of p-type semiconductor material. The emitter, base, and collector define a pair of junctions, namely a collector-base junction and an emitter-base junction, across which the conductivity type of the respective semiconductor materials changes. A voltage applied across the emitter-base junction produces charge flow between the collector and emitter.
Improved methods are needed for designing and fabricating bipolar junction transistors.